This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The proposed study aims at defining specific features of antibodies elicited by candidate HIV vaccines that are required for protection from infection. In this study three different candidate HlV vaccines will be tested. The groups of animals will be immunized with one of the three vaccines (three immunization groups and a fourth that will serve as un-immunized control group) and then exposed to SHIV. The immune responses against the virus will be monitored before and following viral-exposure. It is anticipated that the immunized animals will be able to better control viral replication;in fact some animals may be completely protected from infection, than the control animals, A this stage however, we do not know which of the three candidate vaccines will elicit the more protective anti-viral responses.